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By C. Chu

An investigation has been made of the radial heat-wave process using a mathematical model in two-dimensional cylindrical coordinates. This model considers combustion, convection and conduction inside the reservoir, but only conduction in the bounding formations. From a study of the general features of the process, an important phenomenon has been revealed, namely, the feedback of heat into the reservoir on the trailing edge of the heat wave. The effects of various process variables on the performance characteristics of the process have also been investigated. It was found that up to the time when the combustion front reaches a given point, the per cent heat loss, provided it is not higher than 40 per cent, is approximately directly proportional to the square root of thermal conductivity arid fuel content, but inversely proportional to the square root of gas-injection rate and oxygen concentration. The effecr of reservoir thickness is more pronounced, since halving the thickness doubles the per cent heat loss. The most decisive factor in determining the center-plane peak temperature is the fuel content of the reservoir. Within the temperature range investigated, doubling the fuel content doubles the peak temperature in the early stage, but the rate of decline of the peak temperature is high. Reservoir thickness is also a very influential factor. The peak temperature is lowered when the thickness is reduced; however, the effect of thickness becomes less pronounced when the thickness is high. Reduction of oxygen concentration increases the peak temperature in the early stage but lowers it afterwards because of the higher rate of decline of the peak temperature. Increase in gas injection rate or decredse in thermal conductivity geives a higher peak temperature which stays high for a longer period. The propagation range of the heat wave is chiefly governed by the fuel content of the reservoir. An increase of 0.2 1b/cu ft in the fuel content increases the propagation range by 100 per cent. The propagation range is more than doubled by doubling the gas injection rate, or reservoir thickness, or by reducing the thermal conductivity by 50 per cent. Comparatively, oxygen concentration has less effect on the propagation range. INTRODUCTION Several investigators have conducted theoretical studies of a radial heat wave. Vogel and Krueger1 studied a system with a moving cylindrical heat source of constant temper- ature, considering conduction in the radial direction only. Ramey2 included conduction in the vertical direction in his studies. Bailey and Larkin2 attacked a more general problem where initial well heating, vertical heat losses and arbitrary frontal velocities were included. In all these studies, however, conduction was considered to be the only means of heat transfer. Bailey and Larkin in a later paper included the effects of convection in a study involving both linear and radial geometries. Vertical heat losses were neglected in the radial case. Katz5 studied a similar problem in a one-dimensional radial model, using a heat-loss coefficient to account for vertical heat losses. Selig and Couch6 mployed a cylindrical model and investigated two limiting cases. In one case they considered no heat loss from the reservoir whereas in the other they assumed a constant temperature at the interface between the reservoir and its bounding formations. Thomas' studied a more general case but assumed a permeable bounding formation so that the convection effect is not confined to the reservoir. In the present work a more realistic and more generalized model is used. It involves a two-dimensional cylindrical system with combustion, convection and conduction inside the reservoir, but only conduction in the bounding formations. The purpose is to establish the temperature distribution both inside and outside the reservoir, to study the general features of the radial heat wave process, and to investigate the effects of various process variables on the performance characteristics of the process. THEORY We fist consider a circular porous reservoir of thickness H extending vertically from y = — H/2 to y = + H/2. The reservoir extends from a well bore radius r, to an external radius re. A stream of oxygen-containing gas is introduced into the reservoir through the wellbore. The oxygen-containing gas reacts with the fuel contained in the reservoir and forms a combustion front wherever the prevailing temperature can support the combustion. It is here assumed that this combustion front constitutes a cylindrical surface source of heat having an infinitesimal thickness in the radial direction and extending vertically throughout the whole thickness H. This is designated as Region I. We next consider a Region II corresponding to the upper and lower formations bounding the reservoir, extending from y = — - to y = — H/2 and from y = + H/2 to y = + m. Since r, is very small, we may assume that the two bounding formations have the same dimensions, symmetric with respect to the center plane of the reservoir. In this way, we may take the upper half of the system alone into consideration. In contrast with

By Wang Shulan

The synthesis process of BaTiO3 from TiO2 and BaCO3 in the molten NaOH-KOH at 350oC was studied by the A.C impedance technique. The A.C. impedance of molten NaOH-KOH (xNaOH = 0.36) and the variation of the conductivity of the salt with time during the synthesized process were measured. The synthesized reaction of the BaTiO3 and the decomposition reaction of BaCO3 are fast and were finished in 10min. The interaction between TiO2, BaO and BaTiO3 and the molten salt was confirmed by the variation of the conductivity.

Jan 1, 2005

Although bismuth mineralization is spread widely through the Lachlan Fold Belt in New South Wales, broad grouping of the various deposits can be effected on the basis of geographical and geological (age and type of associated rocks) affinities. As a result, significant concentrations of bismuth can be recognized in the Mid-Western granites, Cobar-type ore, the Yass Silurian acid volcanic belt, and the Albury, Bega, Braidwoodand Bathurst districts.In these deposits bismuth generally occurs in minor amounts associated with molybdenite, wolframite, scheelite, cassiterite, chalcopyrite, galena, magnetite, pyrite, arsenopyrite, and native gold. From this group of minerals three broadly defined associations can be recognized.I. Bi-Sn-W-Mo2. Bi-Au( -Te)3. Bi-Pb-Cu(-Au)There may be some interchangeability of these metals, as instanced by occasional Bi-Cu-W-Mo mirleralization, but pyrite and/ or arsenopyrite are usually prominent in all associations.The first two of these associations occur mainly in the form of narrow quartz veins rarely averaging more than O· 3 per cent Bi, although there is often a marked enrichment in ferruginous material in the oxidized zone.Most of these veins occur within or adjacent to granitic rocks of varying ages (principally Silurian or Devonian), although Bi-Au mineralization tends to be related to more basic igneous activity than the Bi-Sn-W-Mo association.The latter is also occasionally developed in pipes, usually coarse-grained and richer in bismuth (as at Whipstick, the principal mine in New South Wales with a production of 343 tonnes of the metal), or in lower grade, but probably larger tonnage skarn deposits. The bismuth-base metal association occurs mainly in Silurian acid volcanic sequences and may also form low grade but large tonnage deposits, such as is possibly developed at Cobar.

Jan 1, 1973

By H. K. Taylor

Ore reserves are inadequately defined. Geological reconnaissance and pre-feasibility mining work generate a broad range of valid tonnage estimates, many published for the benefit of various interests, who may view all figures as reserves. This work reviews the regular estimation of tonnages, grades and relevant factors for single deposits. A consistent framework of definition is suggested which, by conforming to the known structures of feasibility studies and long-range plans, avoids the pitfalls of over-categorisation and of unrealistic promises. Applications are based on North American experience but are intended for general use

Sep 1, 1991

By Tom Barczak

Early in my career, while giving a presentation on shield design for longwall mining at one of the International Conferences on Ground Control in Mining, the late Jim Scott told me that I was finally getting it, because ?I was starting to think like a rock!? Although I didn?t realize it at the time, those few words changed my career forever. At the start of my career, I did a lot of laboratory testing, taking advantage of the unique capabilities of the Mine Roof Simulator to study the performance and design characteristics of longwall shields. I had a pretty good handle on what made shields work and what made them fail, but I was still struggling with how and why they develop their in-service loads and what they were actually controlling as opposed to being passive bystanders in a world beyond their control. It became clear to me that the simplistic models of dead weight loading could not explain the behavior I saw and measured underground. The problem did not go away when I started studying standing support systems. Again, I learned much about the strength, stiffness, and stability of these supports and helped the industry develop several new support products that attempted to provide more efficient support designs. But here, too, the simplistic models of dead weight loading did not seem to fit for me. That?s when I began to incorporate the ground reaction concept as a way of integrating the support response and the ground behavior into a cohesive design methodology. The concept has its limitations, no doubt, but I believe some form of it will be the future of not only designing supports but also, in the broader sense, enhancing the engineering aspects of ground control. The paper presented at the International Conference on Ground Control last year by Esterhuizen (2010) on pillar behavior is evidence of this. Think like a rock. Jim Scott was right. It takes two to dance. You can?t dance alone and you will never understand ground control by thinking like a support! ?Dumb as a box of rocks?? I don?t think so. The answer lies in the rocks!

Jan 1, 2011

By R. K. Dann, L. W. Roberts, R. B. Benson

The mechanical properties of 300-series stainless steels were investigated in both high-pressure hydrogen and helium environments at ambient temperatures. An auslenitic steel which is unstable with respect to formation of strain-induced a (bee) and € (hcp) mar-tensile is embrittled when plastically strained in a hydrogen environment. A stable austenitic steel is not embriltled when tested under the same conditions. The presence of hydrogen causes embrittlement at the mar-lensitic structure and a definite change in the general fracture mode from a ductile to a quasicleavage type. The embrittled martensitic facets are surrounded by a more ductile type fracture which suggests that the presence of hydrogen initiates microcracks at the martensitic structure. If a steel is unstable with respecl to fortnation of strain induced martensile, plastic deformation in a hydrogen environment will produce rapid embrittlement of a notched specimen in comparison to an unnotched one. FERRITIC and martensitic steels can be embrittled by hydrogen that has been introduced into the alloys, either by thermal or cathodic charging prior to testing.1-5 However, conflicting reports exist as to whether austenitic steels that are stable or unstable with respect to formation of strain-induced martensite can be embrittled by hydrogen.8-12 A recent investigation has shown that cathodically-charged thin foils of a stable austenitic steel can be embrittled.13 An earlier investigation of a thermally charged 18-10 stainless steel revealed a significant decrease in the ductility only at the lowest test temperature of -78°C, although strain-induced bee martensite was shown to be present in one specimen tested at ambient temperatures.' When martensitic steels are tested in a hydrogen atmosphere, they are embrittled.'4-'7 It has been observed in this Laboratory that 304L steel, which is unstable with respect to formation of strain induced martensite, forms surface cracks when plastically strained in a high-pressure hydrogen environment. Work in progress elsewhere concurrent with this investigation has also established that 304L is embrittled when tested in a high-pressure hydrogen atmosphere." The objective of this investigation was to study the effect of a high-pressure hydrogen environment on the tensile properties of a stainless steel that contained strain-induced martensite (304L) and one that did not (310). EXPERIMENTAL TECHNIQUES Notched and unnotched cylindrical specimens were machined from 304L* and 310 rods that were heat- treated at 1000°C in argon for 1 hr followed by a water quench. The chemical analyses of these steels are given in Table I. The unnotched specimens had a reduced section diameter of 0.184 & 0.001 in., a gage length of 0.7 in., and were threaded with a 0.5-in.-diam. thread on each end. The notched specimens had a reduced section diameter of 0.260 * 0.001 in. and a 0.75-in. gage length, with a 30 pct 60 deg v-notch at the center. The notch had a maximum root radius of 0.002 in. The tensile bars were fractured in a hydrogen or helium atmosphere of 104 psi at ambient temperatures. The system used for mechanically testing the specimens is to be described in detail elsewhere.19 Several specimens of each type were tested in air using an Instron testing machine. The same yield strength and ultimate tensile strength were obtained in 104 psi helium with the above system as with the conventional testing machine. Magnetic analysis was employed to determine that there was a (bee) martensite in plastically deformed 304L and that it was not present in plastically deformed 310. The magnetic technique depended on allowing the material being studied to serve as the core between a primary and secondary coil. Thus, any change in the amount of magnetic material present between the annealed and plastically deformed steels will be indicated by corresponding changes in the induced voltage in the secondary circuit." The ratio of the output signal of a nonmagnetic stainless steel to a completely magnetic maraging steel was 2000 to I. Several unnotched 304L bars tested in hydrogen were analyzed for hydrogen by vacuum fusion analysis. There was an increase in the hydrogen content to approximately 2 ppm for the specimens tested in hydrogen, as compared to less than 1 ppm for the as-received material. Several thin sections cut from notched areas of 304L specimens tested in hydrogen and containing the fracture surface contained approximately 1.5 ppm H. The accuracy of these determinations was estimated to be ± 50 pct.

Jan 1, 1969

By M. Nicholas, D. M. Poole

The diameters of sessile drops have been found to increase linearly with time in five reacting binary metal systems. The spreading rates of the drops are markedly dependent on temperature and on prior alloying of the solid with the lower melting point metal, hut are independent of the drop volume, wetting atruosphere , solid-surface roughness, and prior alloying of the drop with the substrate metal. A mechanism has been suggested that relates the linear-spreading rate to lateral diffusion of the liquid-metal atoms into the solid at the drop edge. An Arrhenius- type equation has been derived that describes the temperature dependence 0) the spreading rate, and although the agreement between the actual and the predicted pre-exponen-tial terms is poor that between the activation energies is excellent and the variation in the spreading rate of copper on Ni-Cu alloys produced by different extents of alloying can be predicted with considerable accuracy. CHEMICAL interactions frequently change the wetting behavior of solid-liquid systems causing, for example, "secondary spreading1 of sessile drops beyond the size defined by the surface and interfacial tensions of the unreacted components. The kinetics of the contact-angle decreases associated with this spreading are similar for many systems, but few studies have been made with the objective of determining whether the similarities are a reflection of a common mechanism. Some workers2,3 have assumed the secondary spreading is controlled by changes in the liquid surface and liquid-solid interfacial tensions and hence by the composition of the liquid, and contact-angle changes measured by the vertical-plate technique have been used to follow the course of liquid-solid chemical reactions.4 Other processes that have been invoked to explain these time-dependent changes in specific systems include the removal of adsorbed gas from the liquid-solid interface.5 penetration of containment layers on the solid Surface,6 interdiffusion,1,7 reori-entation of the solid surface into a wettable configuration: vapor-phase transport of the liquid onto the solid in advance of the drop,9 and, from vertical-plate studies. capillary flow between oxide layers and the solid surface.10 One of the reasons for the profuseness of these suggestions may be the complexity of the contact-angle change kinetics. However, in an analysis of secondary spreading gold and copper on UC,11 it was found that the diameter of the contact area between the sessile drop and the solid surface showed a simple linear increase with time although contact-angle changes were more complex. To check whether the linearity was merely fortuitous! additional exploratory work was conducted with four reacting metal-metal systems: Au on Ni. Cu on Ni, Cu on Fe, and Ag on Au. Linear spreading was observed in every case even though the kinetics of the contact-angle changes were complex. A further detailed study of the kinetics of linear spreading of five reacting metal-metal systems has been made with the object of determining the mechanism involved. The influence of variables such as temperature, drop volume. and the initial composition of the drop on the linear-spreading rate has been measured and compared with those predicted by a number of possible mechanisms. The systems employed in this study (Cu and Au on Ni and Pt, and Ag on Au) were selected because of the availability of potentially relevant chemical and physical property data. the simplicity of their phase diagrams at the wetting temperatures, and the ease of experimentation. EXPERIMENTAL TECHNIQUES The purities of the metals used in the study were: copper, 99.9 pct; gold. 99.96 pct; nickel, 99.2 pct; platinum 99.99 pct; and silver, 99.999 pct. The wetting tests were performed in a split tantalum tube vacuum resistance furnace of a conventional design. The furnace element was held vertically and was 1 $ in. in diam and 6 in, long. Viewing ports were provided in the water-cooled chamber to enable the specimens to be observed in both the horizontal and vertical planes. The temperature in the hot zone of the furnace could be held at 1500" i 5°C for an indefinite time. The surfaces of the solid-plaque metals were ground flat on Microcut paper and both the sessile drop and substrate metals were ultrasonically cleaned in methyl alcohol prior to their insertion in the furnace. After loading, the furnace was pumped down to a pressure of 2 x 10-5 mm of mercury and degassed for 30 min at 900° to 950°C. The temperature was then increased at more than 100°C per min to that used in the wetting test. The vacuum at the wetting temperature was better than 5 x 10-5 mm of mercury. Dewetting and retraction of the drop on cooling did not occur and the contact-area diameters, therefore, were measured after solidification with a vernier traveling microscope. The diameters quoted later are arithmetic means of ten measurements. The standard error of the mean never exceeded 3 pct and was often less than 1 pct.

Jan 1, 1967

By Pablo Andrés Galarza

Si bien la ventilación de minas depende de las condiciones de la naturaleza, en muchos casos, la profundidad de las mismas, requiere de un sistema completo de ventilación forzado. En este sentido, el texto señala el uso de dicho sistema y sus implicancias como la ubicación de la ventilación principal, número de ventiladores auxiliares y otros medios de control como reguladores, tampones y costos de operación. Asimismo comprende la determinación de un método apropiado para la solución de la red y la selección de un sistema económico más efectivo con los objetivos, parámetros e incentivos de la mina.

Nov 8, 1982

By C. Carreno, A. D. Gonzalez Escarcega, M. A. Neri, A. Martinez –Villafane, O. Cobarrubias-Alvarado

"Waspaloy is a superalloy used to manufacture some aeronautical parts subjected to high temperatures and stresses. During thermo-mechanical processing cracks are generated, causing some parts to be rejected. In order to determine the causes of these cracks, this alloy was characterized using techniques such as chemical analysis, optical microscopy, scanning electron microscopy, and EDX analysis. Heterogeneous grain sizes in the microstructure cause a non-uniform strain distribution in these parts, creating cracks in zones with different grain sizes.IntroductionNickel-base superalloys are important materials for high-temperature service applications. The manufacture of components from these materials is typically based on solidification or powder-metallurgy processes [1]. Solidification techniques comprise either the direct casting of parts or the casting of ingots which subsequently undergo a series of thermo-mechanical-processing steps to refine the microstructure. During solidification, microsegregation is usually unavoidable. The primary solidification product is a disordered nickel solid solution with an fee crystal structure (?). In many alloys, the material which solidifies last is a mixture of ã and an ordered fee phase (? '). In prototypical nickel-base superalloys, the ?'-phase is Ni3(Al,Ti) [2-3].Waspaloy is a superalloy that is used in demanding high-temperature environments in which good creep and fatigue resistance are required. One of the most common applications of Waspaloy is for turbine engine rings. To ensure the required mechanical properties, the rings are usually forged and heat treated (Figure 1). Two distinct types of microstructures are usually found to be attractive for such applications: a) A microstructure with a grain size of ASTM 10 to 14 for tensile strength, ductility, and resistance to crack nucleation in low-cycle fatigue; or b) A microstructure with a grain size of ASTM 4 to 8 required for creep strength and resistance to crack propagation [4]. Because it is impossible to refine the grain size through heat treatment, a skillfully designed forging process is crucial for the control of the grain size and, hence the properties of the forged ring [5-6]."

Jan 1, 2012

R. G. BROWN, Bodie, Cal.: Mr. Rickard's paper, with its valuable illustrations, brings into fresh clearness the game of hide-and-seek which the miner must play with his ore-deposit; but, more than this, it goes far towards classifying those perplexing idiosyncrasies which, while unclassified, constitute a labyrinth almost without clue. Probably every engineer can add to the list by the mention of at least one fresh detail from his own experience, and I for one would like to comment on two of Mr. Rickard's divisions. To what he has written about " walls within walls" and " walls without walls," the accompanying Figs. 1 and 2 may be appropriate, the more so as they represent conditions obtaining in a part of the Butte copper-belt more typical of the copper-veins as a whole than the Gagnon, which, in some respects the most interesting mine in the camp, stands almost alone in many particulars. (See nuns., xvi., 62.) Fig. 1 was sketched in January, 1895, in the stopes above the 700-foot level of the Colusa-Parrot mine, east of the Parrot and southwest. of the Anaconda. The stope, the commercial foot-wall of which is shown at A, was 30 feet wide at this section, the pay-ore being massive chalcocite, jumbled with bornite, pyrite, quartz and thoroughly broken-down granite. A and At are inch-thick seams of black talc; B, B' and B" are also talc, possibly 1/8-inch thick. In the plane of the section the "banded quartz " and " quartz and pyrite " were both of too low grade for extraction, but 5 feet back along the stope had been of fair value. The granite with quartz and bornite between Bt and A' was pay-ore, but that to the right of B" was not. In both cases the ferro-magnesian minerals had been removed, leaving, where not obscured by ore, faint, dark patches. Between A'

Jan 1, 1897

Operation of the tankhouse at the Electro lytic Refining and Smelting Company's works has been improved, but further automation is re- quired to cut the labour intensive nature of the routine tasks. Anode quality, both chemical and physical, plays an important role in efficient refinery practice, and impurities such as lead, antimony and nickel have required careful monitoring for smooth operation. The gradual replacement of copper blanks by titanium has markedly improved the quality of starting sheets, but problems have been ex- perienced with surface preconditioning of the titanium blanks. Polishing with emery paper proved to be a successful technique.

Jan 1, 1976

By Dirk van Zyl, S. Chander

Minerals have been critical to human society from the earliest and their use has been intertwined with the development of civilization. In the Western World, the mining, processing and extractive metallurgy associated with ores was first described in detail by Agricola in the 16th century. He considered these collective activities to be the most necessary and the most profitable of professions, and wrote, "without doubt, none of the arts is older than agriculture, but that of the metals is not less ancient; in fact they are at least equal and coeval, for no mortal man ever tilled a field without implements. In truth, in all works of agriculture, as in the other arts, implements are used which are made from metals, or which could not be made without the use of metals; for this reason the metals are of the greatest necessity to man." Ours is still a materials-dependent society that relies heavily on minerals for raw materials. Today our dependence on minerals is exceptionally great. To meet the need for fuel and non-fuel minerals in a representative year, in the United States alone, about one billion tons of coal and 2.7 billion tons of ore are mined. These mineral products are essential for fertilizers, for construction materials, metals and alloys, for manufacturing household and industrial items, for transportation, and for the generation of electric power. It is instructive to consider the diversity of uses found in our society for a single mineral product - silver, for example. Experts believe that in the past 5000 years we have mined about a million tons, or 31.9 billion troy ounces of silver. In 1988, 133 million troy ounces of silver were used in the Unites States. Most of the silver used was for techno- logical, medicinal and industrial purposes, Table 1. X-ray films, for example, carry comparatively large amounts of silver to lessen patient's radiation exposure. Silver does not prevent tooth decay, but each year about two million troy ounces of silver is used for dental work in the United States. In small quantities it is used in medicine. No metal - not even copper conducts heat and electricity so efficiently as silver. Silver wires lace solar cells, and silver oxide batteries power hearing aids, calculators, submarines and satellites. Hardened with tungsten or molybdenum, miniature discs of silver pass current from wire to wire in cars, telephones and computers. A dish- washer timer alone may have 50 such electrical contacts, which open and close without excessive heat or friction. Silver is an important component of solar reflectors, since no other material reflects light so well or uniformly. In our personal lives, silver remains in high esteem to adorn our tables, provide precious objects and jewelry. In many parts of the world, silver in the form of coins, jewelry and bullion is used for financial independence and security against the vagaries of paper currency. In India, silver is used in its purest form as thin foils to decorate sweets and other edibles. It is obvious that this mineral product, silver, is of great value and utility in our society. Minerals and Environment The benefits of minerals do not come without problems. Much of the silver, for example, lies locked up in copper, lead-zinc or precious metal ores; to extract it creates vast quantities of waste material. On the average, in order to recover one ounce of silver about a quarter ton of ore must be mined. To meet the world's annual demand for silver, approximately 100 million tons of waste is generated every Year. The problem with silver is repeated with all minerals. Conversion of mineral ores into usable materials necessitates the generation of large quantities of waste products that create tremendous disposal problems. In addition to waste material discarded during mining, wastes may be generated during processing as gases, liquids or solids that must be subsequently converted into forms more acceptable for disposal. Associated with the handling, treatment and management of waste products are a number of environmental problems. Environmental problems are not new to the minerals industry. In his Geographia, Strabo (63 B.C. - 20 A.D.), gives an account of the conditions of labor under which men

Jan 1, 1992

By Thiago Viana de Oliveira Turra

Foi estudado o comportamento do resultado de dureza com o acréscimo de tempo de patamar de tratamento térmico para alívio de tensões, em juntas soldadas com processos MAG e TIG. Utilizou-se o metal base ASTM A743 CA6NM, um aço inoxidável martensítico usado na fabricação de rotores para geração de energia hidroelétrica, e o consumível de soldagem AWS A5.9 ER410NiMo. No processo MAG, foi usado o gás mistura de 96% Ar + 4% CO2, e no processo TIG o gás 100% Ar. Para cada processo, foi soldado um corpo de prova, que foi cortado em sete fatias ao longo do comprimento. Observou-se redução na dureza do estado “como soldado” para o primeiro ciclo de oito horas de patamar. Nos demais ciclos a variação encontrada não tem significância dentro da dispersão da amostragem.

Oct 30, 2017

By E. V. Cilento, K. A. DiGregorio, R. C. Lantz

"DIGREGORIO, K. A., E. V. CILENTO, AND R. C. LANTZ. A kinetic model of superoxide production from single pulmonary alueolar macrophages. Am. J. Physiol. 256 (Cell Physiol. 25): C405-C412, 1989.-A kinetic model was developed to describe the production of superoxide (02) by single pulmonary alveolar macrophages (PAM). Model predictions were compared with experimental results obtained from single rat PAM. The 02 was quantified by measuring the reduction of nitro blue tetrazolium (NBT) to a diformazan precipitate (NBTH,) from video-recorded images of individual cells. The kinetic model considered three reactions: 1 ) the production of extracellular 02 from the reduction of oxygen by NADPH oxidase using intracellular NADPH as the substrate, 2) the subsequent dismutation of 02 to form H,O,, and 3) the reaction of 02 and NBT to form diformazan. NBT specificity for 02 was analyzed by comparing results in the presence and absence of superoxide dismutase (SOD) that catalyzes the dismutation of 02 to H,O,. Measured PAM heterogeneity was accounted for by varying the concentration of intracellular NADPH, its rate of depletion, and the concentration of intracellular NADPH oxidase in the kinetic model. Model predictions compared favorably with experimental results except when SOD was present. This discrepancy may be due to diffusional limitations because NBT is a relatively small molecule (818 mo! wt) compared with SOD (34,000 mol wt). In addition, the cell surface is both ruffled and negatively charged, which may introduce steric hindrances and/ or electrostatic effects, since SOD is also negatively charged, whereas NBT is positively charged.PULMONARY ALVEOLAR MACROPHAGES (PAM) protect the lungs by phagocytizing foreign debris and bacteria. This process is accompanied by the production of superoxide anion (02) at the surface of the plasma membrane (3, 31). Superoxide readily dismutates to form H20 2 and subsequently, other oxygen metabolites which have been shown to be both antibacterial and cytotoxic (21, 25, 35).Superoxide is produced from the reduction of extracellular O, at the surface of the cell membrane by NADPH oxidase by the following reaction (3, 4)"

Jan 1, 1989

By J. Stowe

"While there has been continual improvement in the models for predicting deposition velocity and pipeline friction losses, the fundamental design philosophy for tailings pipelines has remained the same over the previous three or four decades: design the tailings pipeline to operate in turbulent flow without a deposit on the pipe invert for all expected process conditions. Recent improvements in the understanding of slurry pipeline flows allows for the design of pipelines operating with a deposit on the pipe invert, allowing the system to operate at moderate velocities for high flow rates, optimizing system energy requirements and maximizing pipeline wear life.Tailings pipelines are increasingly operated at higher solids concentrations when there is a greater likelihood the pipeline will operate in laminar flow due to the higher tailings slurry rheology. Historically, slurry pipelines have been operated in turbulent flow. We now know that laminar-flow pipeline operation is possible as there are several operational laminar-flow tailings pipelines. While our understanding of laminar-flow slurry pipelines is not complete, recent research provides guidance on how to approach the design of these pipelines.New sensor technology has led to the development of an instrument that provides reliable indication of bed-deposit height within a pipeline. This technology is particularly helpful in operating pipelines with a deposit and has application in better understanding the operation of laminar-flow pipelines. Failure of tailings pipelines can result in consequent damage to surrounding structures and unacceptable spillage into the environment. Modern pipeline leak detection technology allows operators to better manage this risk by ensuring safe and reliable operation of tailings pipelines.This article provides an overview of the each of the above advances in the design and operation of tailings pipelines.Operating tailings pipelines with a depositTailings pipelines, and slurry pipelines in general, are typically designed to operate without a deposit on the pipeline invert. Meaning, the minimum operating velocity exceeds the turbulent deposition velocity. This approach has been adopted due to concerns regarding potential blockage of a pipeline operating with a deposit."

Jun 1, 2019

By C. M. Dentan

Conventional testing of crude kaolin ores emphasizes physical properties as they relate to end uses of kaolin products. This approach to evaluating crude ores does not reveal the basis of behavioral differences between typical coarse and fine kaolins from central Georgia. Optical and scanning electron microscopy in combination with XEDS have been employed to characterize both coarse Cretaceous and fine Tertiary kaolin in order to shed light on the reasons for the gross differences in their properties. Routine evaluation of various parameters was also carried out. Bulk densities were 1.48 g cc-l for the coarse clays and 1.53 g cc-1 for the fine clays. Surface areas were 15 m2 9-1 and 25 m2 9-1, respectively. Brookfield viscosities were low for the coarse clays at 70% solids, and high for the fine clays. The situation was reversed for Hercules viscosities. Sixty percent of the coarse clays had particles of less than 2 um and the fine clays had 90% less than 2 cm. Micrographs of thin sections prepared from blue-dyed epoxy-impregnated crude ores and of SEM fabric samples demonstrated vivid differences in texture. Cretaceous kaolins appeared to be completely recrystallized residual products of former aluminous sediments, while Tertiary kaolins retained their essentially sedimentary character. Differentiation of the coarse and fine kaolins is rapidly accomplished by both optical and scanning electron microscopy, and should be considered a valuable analytical technique in evaluating kaolin ores.

Jan 1, 1981

By D. Rahal, I. Shah, B. Hines, S. Reddick

"The development of stirred milling technology has proven to be an enabling technology in fine grained metallic deposits. The increased grinding efficiency allows for the economic size reduction required to produce saleable concentrates. This improvement has opened the door to retreatment projects such as reprocessing of historic gold mine tailings. Recently a VXP2500 stirred mill was installed at Casmyn Mining Zimbabwe Turk mine to allow the reprocessing of historic mine tailings. After commissioning, an extensive joint research project between Casmyn and FLSmidth Minerals was conducted to optimize the performance of the mill. This paper outlines the challenges encountered in the optimization program and the outcomes from the joint research project.INTRODUCTION The development of stirred mills has opened up many new opportunities to recover valuable minerals from refractory ores. Stirred mills have already been reported as an enabling technology for the processing of fine grained ores in lead/zinc applications (Pease, Young and Curry, 2005). Historically, conventional ball mills were unable to economically grind material fine enough to produce the required recovery or concentrate grade. This often resulted in the loss of valuable materials to the final plant tailings. The advent of stirred milling has now provided an opportunity which has both economic and environmental benefits, the reprocessing of historic mine tailings. Many tailings stockpiles now contain economic concentrations of gold because of the ability of stirred mills to efficiently and economically grind the tailings to liberation sizes. The primary advantage of reprocessing historic tailings is very low cost processing. Recovering the tailings is usually as simple as pumping the material into the reprocessing circuit. The disadvantage of reprocessing tailings is the low feed grade and greater difficulty in recovery valuable minerals at the same size distribution. The material has already been previously processed so fresh surface area or an increase in metal exposure is required. These are both provided by regrinding the tailings material."

Jan 1, 2014

By P. D. Rao

Chemical and physical properties of typical low-rank coal (LRC) ash are significantly different than bituminous coal ash. With the exception of extraneous ash, which is incorporated during mining or is due to ash partings within or between coal seams, LRC ash consists primarily of inherent ash that is bonded into the coal's organic matrix or finely disseminated mineral matter. This paper reviews the nature of LRC ash, both inherent and extraneous, and how this impacts the prospects of washing and utilizing LRCs. A literature review, as well as washability data, proximate and ultimate analyses and ash analysis of 25 Alaskan LRC seams are used as a basis for this discussion. The authors' recent research into the nature and distribution of phosphorous in an Alaskan LRC is also discussed

Jan 1, 1997

By M. Save, N. Menad

"This paper gives the overview of different alternatives to recycle the following wastes: slag, dusts, wastes of electric and electronic equipment (WEEE) and auto shredder residues (ASR). Based on modified Bogue calculations, steelmaking slags were combined in order to produce a belite-rich clinker activated with sulphoaluminate. The EAF dusts containing significant amount of metals can be recycled in different ways: The carbothermal treatment and INTECT process are reported. The results obtained from the model of Auto Shredder Residue injection into blast furnace show that ASR can be used as reducing agent in the BF process if certain conditions are met. The particle size of this material must be controlled to ensure optimal gasification of the material in raceway. The non-ferrous contents may affect the pig iron quality, which is difficult to rectify at a later point. It seems the pyrolysis is the most attractive process to handle ASR. The BRGM flow sheet of WEEE treatment is also reported.I. Introduction The activities of human been may generate wastes and by their accumulation during several years, these wastes may have an impact on the environment and on the human health. These wastes can be generated in the forms of solid, liquid and gas. A variety of industrial wastes can be recycled for use as products. There are three ways in which industrial waste recycling occurs: at the facility itself (on-site recycling), at commercial facilities that gather waste streams from several companies (off-site recycling), and at a company that uses as inputs in its production process the waste products of another company. The industries producing iron and steel may generate different solid wastes which are classified in three main categories: 1. Ferrous material (mainly dusts and sludges from gas cleaning), 2. Slags (these by-products are generated from different process stages), 3. Others by-products (including refractories and material generated from engineering activities). According to this review, the most quantity of the metallurgical wastes is deposed. Currently, the public opinion opposes the creation of new sites. This leads to the growth of the waste disposal costs. Such situation reduces the enterprise competitiveness and decreases their market share on regional and/or national and/or world scales. In these conditions, the economical activities can be decreased leading probably to social problems. The problem of wastes and/or by-products can be treated on three levels:"

Jan 1, 2008

In 2011, the value of mineral production increased in the United States for the second consecutive year (Table 1). Production increased modestly for most mineral commodities mined in the United States, and price increases, especially for precious metals, resulted in increases in the value of production. Minerals remained fundamental to the U.S. economy, contributing to the real gross domestic product (GDP) at several levels, including mining, processing and manufacturing finished products. Minerals? contribution to the GDP increased for the second consecutive year. Trends in other sectors of the domestic economy were similar to those in mineral production and consumption rates. U.S. apparent mineral consumption (industrial) of 11 mineral commodities decreased substantially from 2005 to 2010 (aluminum, cadmium, cement, copper, iron, lead, salt, soda ash, steel, tin and zinc). Data for 2011 were not calculated, but the data show a sustained decrease (especially for the metals) preceding the recession through 2010, so consumption seems to be behaving differently than production and GDP. After continued decline following the 2008?2009 recession, the construction industry began to show signs of improvement during 2011, with increased production and consumption of cement, construction sand and gravel, and gypsum ? mineral commodities that are used almost exclusively in construction. Crushed stone production, however, continued to decline.

Jan 1, 2012